Method of making laminar batteries

ABSTRACT

Thin flat electrical cells and batteries comprising frames formed with a central opening for receiving wet electrical cell components and made from a two layered structure of a high melting thermoplastic material and a lower melting thermoplastic material, and methods of making the same.

This is a division of application Ser. No. 852,919, filed Nov. 18, 1977,now abandoned.

This invention relates to electrical cells and batteries, andparticularly to novel laminar cells and batteries and methods of makingthe same.

Thin flat laminar batteries are commonly made with cells separated andelectrically connected together by conductive plastic intercellconnectors. The cells are completed by liquid impervious borders formedby sealing the inner edges of the intercell connectors to and betweenliquid impervious frame elements. One approach to the manufacture ofbatteries of this kind is to make the frame elements integral with theseparators by filling the borders of liquid permeable separator materialwith a liquid impermeable heat activatable adhesive. Such a constructionis shown and described in U.S. Pat. No. 4,019,251, issued on Apr. 26,1977 to Thomas P. McCole for Flat Battery and Method of Manufacture, andassigned to assignee of this application.

In another construction, shown and described in U.S. Pat. No. 3,907,599,issued on Sept. 23, 1975 to Ralph D. Fanciullo and Ludwig G. Fasalinofor Flat Battery, and assigned to the assignee of this application, theframes are made of vinyl sealed to the borders of the intercellconnectors and current collectors and sealed to themselves to form aliquid tight peripheral seal around the battery.

A third form of construction is shown in Copending U.S. application ForLetters Patent Ser. No. 761,651, filed on Jan. 24, 1977 by Edwin H. Landfor Electrical Cells and Batteries and assigned to the assignee of thisapplication. In application U.S. Pat. No. 4,119,770, frames ofthermpolastic hot melt adhesive material are described to whichcellophane separators are adhered. Conductive plastic intercellconnectors extend between and are bonded to the frames, and the terminalcurrent collectors are similarly bonded to the frames by application ofheat and pressure. A method of making batteries of the kind described inU.S. Pat. No. 4,119,770 is described in U.S. application Ser. No.761652, filed on Jan. 24, 1977 by Gordon F. Kinsman for Flat Batteriesand Method of Making the Same and assigned to the assignee of thisapplication now abandoned.

In the manufacture of batteries of the type described above, care mustbe taken in the sealing process to avoid combinations of heat andpressure that would cause the materials being sealed to flow out ofposition instead of simply being softened and adhesively bonded asdesired. This is particularly true when it is desired to seal pieces ofthe same material together, as in the vinyl-to-vinyl seals described inU.S. Pat. No. 3,907,599 cited above.

One object of this invention is to reduce the tendency of the materialsto flow during sealing in the manufacture of laminar batteries.

Another sealing problem that has been encountered, particularly withbatteries of the kind described in U.S. Pat. No. 4,119,770 cited above,arises from the use of the combination of a wet slurry cathode, gelelectrolyte, and a cellophane separator. As noted above and more fullydescribed in application Ser. No. 761,652, cited above, the cellophaneseparators are initially heat sealed to the thermoplastic frames tofacilitate assembly. When a multiple cell battery is assembled fromthese components, it is difficult to keep the components, particularlythe slurry cathode and gel electrolyte, in position as the componentsare assembled and before they are sealed. This problem can be solvedwith difficulty by forming the seals one at a time as the components areput in place. The difficulty is that a frame material which will adhereto cellophane also has a strong tendency to adhere to the sealingplatens. Another object of this invention is therefore to facilitate thestep by step sealing of laminar batteries. A further object of theinvention is to facilitate the sealing of batteries with very thickframes, or with many cells.

Briefly, the above and other objects of the invention are attained by acombination of structures and methods organized about the use of a frameformed as a two part laminate of a first thermoplastic material that canbe softened over a relatively high temperature range with a secondthermoplastic material that can be adhered to cellophane and softensover a range substantially below that of the first material. A centralopening is formed in the laminated frame to receive cell components, anda cellophane separator is adhered by heat and pressure to the adhesiveside of the frame.

The manufacture of batteries in accordance with the invention preferablyis carried out on a carrier sheet to which have been adhered a series ofdiscrete cathode collector assemblies in the manner described in detailin above cited U.S. Pat. No. 4,019,251, which is hereby incorporatedherein by reference. Each of the cathode collector assemblies comprisesa metal foil cathode terminal adhered to the carrier sheet and aconductive plastic current collector adhered to the metal terminalsheet.

As the process of the invention is applied sequentially to each cathodecollector assembly in turn, attention will be focused on a typical oneof them. On the conductive plastic surface of such a typical cathodecollector assembly, there is first extruded a wet slurry cathode in themanner described in the above cited U.S. application Ser. No. 761,652. Acomposite framed separator as described above is then placed down on thecathode subassembly, with the cellophane separator in contact with andextending beyond the borders of the cathode slurry, and the lowtemperature range thermoplastic in contact with the conductive plasticface of the cathode collector assembly. A layer of gel electrolyte isthen extruded into the pocket formed by the opening in the frame abovethe cellophane separator. Next, a conductive plastic intercell connectoron which a zinc anode has been formed is placed with the zinc inregistry and in contact with the gel electrolyte and the intercellconnector engaging the high range softening side of the frame. Then heatand pressure is applied to the frame sufficiently to activate the lowtemperature adhesive side and bond the frame to the conductive plasticcurrent collector. Next, the conductive plastic intercell connector issealed to the frame. Operation thereafter is essentially repetitive,commencing with the extrusion of a second cathode slurry over theintercell connector.

The apparatus and method of the invention will best be understood byreference to the following detailed description, together withaccompanying illustrative drawings.

In the drawings;

FIG. 1 is a schematic diagram of a presently preferred process formaking a laminate for use in the invention;

FIG. 2 is a schematic perspective sketch of a framed cellophaneseparator in accordance with the invention;

FIG. 3 is a fragmentary schematic perspective sketch illustratingtypical steps in the process of forming a battery in accordance with theinvention;

FIG. 4 is a schematic perspective sketch illustrating the externalappearance of a battery made in accordance with the invention; and

FIG. 5 is a fragmentary schematic sketch, on an enlarged scale and withvertical dimensions exaggerated, illustrating the internal constructionof the battery of FIG. 4 as seen essentially along the lines 5--5 inFIG. 4.

FIG. 1 illustrates a presently preferred mode of the preparation of alaminate for use in the invention. As shown, a conventional extruderprovided with a flat film die 1 extrudes a curtain of hot moltenthermoplastic material 2 through the die onto a web of material 3 drawnfrom suitable source shown as a supply roll 4. An intermediate roll 31maintains the angle at which the sheet 3 approaches the roll 5 as thediameter of the supply roll 4 changes. The joining of the thermoplasticmaterial 2 to the thermoplastic material 3 occurs at, or just before,the ingoing nip of a driven chill roll 6 and a compliant rubber coveredrubber roll 5. A backup roll 30 provides cooling and mechanical pressurebackup to the rubber roll 5.

The chill roll 6 is cooled in a conventional manner, not shown, as byrecirculated cooled water, so that as the laminate advances around theperiphery of the roll 6 in a clockwise sense as seen in FIG. 1, thethermoplastic layers 2 and 3 are sufficiently cooled and toughened sothat the laminate can be stripped from the chill roll 6 by a stripperroll 32. The freed web of the laminate procedes from the stripper roll32 to a driven windup roll 7.

Stripping of the thermoplastic layer 2 from the chill roll 6 requiresthat the interface be cool to reduce its adhesion. To aid in releasingthe laminate, the chill roll 6 is preferably provided with a chromeplated matte surface.

The thermoplastic material from which the sheet 3 is made is chosen tobe relatively dimensionally stable under the conditions of temperatureand pressure at which the layer 2 flows. It should of course bechemically inert to the electrochemical system in which it will beinstalled, and be capable of adhesion to the conductive intercellconnectors to be described, and to the thermoplastic layer 2. Numerousconventional thermoplastic materials will occur to the artisan asmeeting these requirements. A currently preferred material is rigidvinyl sheeting, such as a polyvinyl chloride homopolymer, or acopolymer, such as a copolymer of vinyl chloride and vinyl acetate madefrom 4 to 15 percent by weight of vinyl acetate and 96 to 85 percent byweight of vinyl chloride, based on the weight of copolymer. Typically,commonally available vinyl sheeting materials also contain conventionalimpact modifiers, stabilizers and lubricants. These vinyl sheetingmaterials soften in the neighborhood of 360° F. under moderatepressures. As another specific example of a suitable material, mentionmay be made of Surlyn A.

The thermoplastic material 2 is preferably one that softens underconsiderably lower temperatures, such as a polyamide hot melt adhesivefor which softening temperatures are in the range of 200°-330° F.Ethylene vinly acetate and other similar materials that will occur tothe artisan may also be employed. It will be understood by those skilledin the art that the flow and adhesive behavior of thermoplasticmaterials is a function of pressure and time as well as temperature, sothat the exact temperatures attained during a given sealing process arenot critical, and in fact may vary over a considerable range. Thesignificant point in the selection of the materials for the layers 2 and3 is that the layer 2 should soften and flow under conditions oftemperature and pressure considerably lower than required to soften thesheet 3. In practice, it is preferred to make the sheet 3 two to threetimes as thick as the layer 2; for example, in accordance with onepractice of the invention the sheet 3 was made of American Hoechst vinylsheeting D 18C 8A, 8 mils in thickness,and the layer 2 was made ofVersalon 1140 hot melt adhesive resin as made and sold by General Mills,Inc. of Minneapolis, Minn., coated two to three mils in thickness.

The cooled laminate is formed into frames such as 8 in FIG. 2, as by diecutting an aperture 9 through each such frame, and cutting the sheetinto rectangular pieces. A cellophane separator 10 is then adhered tothe adhesive side 2 of the laminated frame 8, as by heat and pressure orthe like. If desired, the cellophane may be applied over the aperturesbefore the laminate is cut into frames. The sheet 10 may be, forexample, of PUDO cellophane 1.34 mils in thickness, as made and sold byE. I. duPont deNemours & Co. of Wilmington, Del. In view of the adhesivenature of the layer 2 of the frame, it will be apparent that many otherconventional separator materials could be employed, such as thosedescribed for example, in the above cited U.S. Pat. No. 4,019,251.

The invention can be practiced in the manufacture of batteries using anyconventional acid or alkaline electrochemical system, it only beingnecessary that the thermoplastic materials chosen for the frame such as8 be chemically inert in the system chosen. The presently preferredembodiments include zinc anodes, manganese dioxide cathodes, and anelectrolyte of either potassium hydroxide or of mixtures of ammoniumchloride and zinc chloride. Specific compositions that are especiallysuitable for use in the practice of the invention are those described indetail in U.S. application Ser. No. 761,651, cited above, which isincorporated herein by reference. For simplicity and clarity of thefollowing description, the invention will be described with reference tothe latter system. However, it should be understood that the inventionmay be carried out in the manufacture of any laminar battery employingthermoplastic frames regardless of the electrochemical system employed.

Referring to FIG. 3, typical steps in the manufacture of batteries inaccordance with the invention are shown. It is preferred to carry outthe process on an electrically insulative carrier web 12, such asdescribed in detail in the above cited U.S. Pat. No. 4,019,251, to actas a carrier to move the components of the batteries through the variousstages of manufacture as they are assembled.

Various operations are illustrated for conciseness as being carried outimmediately followed by the previous operation. It will be understoodthat this is done merely to illustrate the sequence of operations, andthat more space between operations would generally be required inpractice.

As shown, the sheet 12 has prelaminated thereto a series of cathodecollector assemblies such as 13. As best shown for the cathode collector13 at the right in FIG. 3, each cathode collector assembly comprises athin metal terminal 14 laminated between the carrier web 12 and a sheet15 of conductive plastic, such as Condulon film as made by PervelIndustries, a vinyl film made conductive by the inclusion of carbonblack.

On each of the conductive plastic cathode current collectors 15 is firstextruded a cathode slurry electrode 16 by means schematically indicatedas a cathode extruder 17. Next, one of the frames 8 with a pre-attachedseparator 10 is placed down over the current collector and cathode withthe cellophane separator 10 engaging the cathode and the adhesive side 2of the frame 8 engaging the conductive plastic 15.

Next, the frame 8 just added is heat sealed to the conductive plastic byheated platens schematically indicated at 18 and 19, as in the mannermore fully shown and described in the above cited U.S. Pat. No.4,019,251, under conditions of temperature and pressure selected tocause the activation of the adhesive of the layer 2 to bond the frame 8to the cathode terminal assembly. Following sealing, the platens 18 and19 are separated. If desired, the heating operation may be followed bycooling operations as described in U.S. Pat. No. 4,019,251. The finalseal of the components present may be effected this time, but in generalit is preferred simply to make the seal sufficient to keep the parts inposition and to make the final seal after all of the components are inplace.

Next, a layer of gel electrolyte 20 is extruded into the pocket definedby the opening 9 in the frame 8 above the cellophane, as by a gelextruder schematically shown at 21.

To the assembly produced as just described is added an intercellassembly comprising a sheet 22 of conductive plastic on which there hasbeen preformed an anode 23, such as a dry patch zinc anode of the kinddescribed in the above cited application Ser. No. 761,651. This anode 23is made to correspond in shape with the aperture in the frame 8, and isplaced down in contact with the gel electrolyte 20 with the conductiveplastic 22 engaging the high melting side 3 of the frame 8. Thisassembly is now heat sealed in the manner generally described above byplatens schematically indicated at 24 and 25, preferably with the platen24 heated and the platen 25 not heated so that the heat enters primarilythrough the thin conductive plastic intercell connector 22. This sealingoperation will in general take place at a higher temperature than thefirst sealing operation. For example, if the sheet 3 is of the Hoechstvinyl material described, and the conductive plastic layer 22 is ofCondulon conductive vinyl film, the Condulon film will soften underconditions of pressure and temperature somewhat below those at which thesheet 3 will soften, so that the primary adhesion mechanism depends onthe softening of the conductive plastic to adhere it to the vinyl sheet3. As typical sealing conditions, mention may be made of a 0.8 seconddwell with the platens 24 and 25 exerting a pressure of approximately 18pounds per square inch on the components, with the upper platen 24 atapproximately 500° F.

Subsequent operations are primarily repetitive of those just described,beginning with another cathode layer 16 being extruded onto the surfaceof the conductive plastic intercell connector 22.

Referring to FIG. 4, showing a completed battery 30, final steps includethe application of an anode terminal assembly generally designated 13,in the manner described in U.S. Pat. No. 4,019,251, which is preferablyprovided with an anode flap 32 folded around to the other side of thebattery and suitably insulated from the cathode in the manner and forthe purposes described in copending U.S. application for Letters PatentSer. No. 782,836, filed on Mar. 30, 1977 by Albert L. Hyland and RobertG. Keene for Laminar Batteries and assigned to the assignee of thisapplication, now U.S. Pat. No. 4,086,399.

FIG. 5 shows an enlarged cross section through such a battery 30 withthe corresponding cell components being given the suffixes a, b, c and dto distinguish the several cells. As indicated in FIG. 5, as the firstframe 8a is pressed down over the cathode assembly comprising theconductive plastic sheet 15 and its cathode slurry layer 16a, thecellophane separator 10a is deformed upward to follow the cathode slurryas the adhesive side 2a of the frame 8a is pressed into engagement withthe conductive plastic 15. Typical dimensions in thickness for thecomponents are about 5 mils for the carrier web 12, 2 mils for the steelor aluminum terminal 14, 2 mils for the conductive plastic layer 15, 2mils for the adhesive layer 2a, and 8 mils for the vinyl frame portion3a. During sealing, heat may be preferentially supplied by the upperplaten 19 in FIG. 3. Alternatively, as the central region of platen 18is arranged to be cooled, as with chilled water, and the outer peripheryof the platen heated, a more efficacious approach would be to heat theassembly from the carrier web side, so that the surface of the adhesivelayer 2a engaging the conductive plastic layer 15 would be hotter thanthe side adjacent the frame element 3a. The reason for cooling thecentral region of the battery during this operation is to dissipate heatconducted laterally through the metal terminal sheet 14.

Referring to FIG. 5, after the first layer 20a of gel electrolyte hasbeen extruded into place in the pocket formed in the opening in theframe 8a, and the conductive plastic intercell connector 22a with itsanode 23a has been put in place, it will be seen that a more efficaciousheat transfer situation is provided when the upper platen 24 in FIG. 3is heated and lower platen 25 is not heated, or is cooled. Preferably,as described above, the central region of the upper platen 24 is alsocooled. The hot surface of the platen engaging the upper surface of theconductive plastic intercell connector 22a is now only 2 mils away fromthe upper side of the frame element 3a where the desired sealing surfaceexists. Thus, the conductive plastic layer 22a may be heated to asealing condition without bringing the bulk of the frame 3a near itssoftening condition.

The situation is somewhat different when the second and subsequentframes such as 8b are added. Considering the frame 8b, when it is put inplace it is desirable to heat the outer periphery of the upper platensuch as 19 in FIG. 3 while cooling the central region, and not to heatthe lower platen such as 18. The reason is a materially shorter heattransfer path between the upper surface of the frame element 3b, and thedesired sealing interface with the adhesive layer 2b and the conductiveplastic layer 22a. As a final sealing operation, with the frame 8d inplace and the anode terminal assembly 31 in position, the heated upperplaten such as 24 in FIG. 3 is employed against the anode collector 31.As shown in FIG. 5, the anode terminal subassembly comprises aconductive plastic layer 33 on which an anode 23d is applied. Theconductive plastic layer 33 is laminated to a steel or aluminum anodeterminal 34. A glassine overwrap may also be employed, as described inthe above cited U.S. Pat. No. 4,019,251.

While the invention has been described with respect to the details ofvarious illustrative and preferred embodiments and practices, manychanges and variations will occur to those skilled in the art uponreading this description, and such can obviously be made withoutdeparting from the scope of the invention.

Having thus described the invention, what is claimed is:
 1. In theprocess of making a laminar battery, the steps of extruding a slurryelectrode onto a central region of the surface of a conductive plasticsubstrate, adhering a separator to a first side of a laminated frame oflarger area than the separator and formed with a central opening adaptedto register with and receive said electrode with the separator extendingover said opening and beyond the border of said opening and the framehaving border portions extending beyond the border of the separator,said frame being a laminate of two heat activatable thermoplasticadhesive materials, a first of said materials on said first side of theframe being adhesively activatable at a first temperature below thetemperature at which a second of said materials is adhesivelyactivatable under the same conditions of applied pressure and durationof heating, said separator being adhered to said first side of saidframe by heat and pressure for a time sufficient to activate said firstmaterial but not said second material, placing said frame and saidseparator adhered thereto over said electrode and conductive plasticsubstrate with said electrode within said opening and said separator inregistry and in contact with said electrode and extending beyond theborders of said electrode and said first side of said frame being incontact with said conductive plastic substrate beyond the borders ofsaid separator, and adhering said frame to said conductive plastic bythe application of heat and pressure for a time sufficient to activatesaid first material but not said second material.
 2. The process ofclaim 1, further comprising the steps of extruding a quantity of gelelectrolyte into the opening in said frame over the separator, placing aconductive plastic intercell conductor having a second electrode formedover a central region of a first surface thereof corresponding in sizeand shape to said slurry electrode over said frame with said first sideof said intercell connector in contact with said second material of saidframe and said second electrode in contact with said gel electrolyte,and adhering said intercell connector to said frame by heating saidintercell connector under pressure to a temperature sufficient to bondsaid intercell connector to said frame while maintaining said first sideof said frame below the temperature at which said first material wouldflow.